To summarize, this was a 5-year-old sickle cell disease (HbSS) patient already on amoxicillin for right-sided otitis media who had ongoing fevers for 6 days and presented with new onset cough. A lung ultrasound was performed and the following images were obtained.

For question #1, 52% of you guessed correctly that there was hepatization of the lung. There were no b-lines (29%), a-lines (16%) or lung point (3%).

For question #2, 65% of you guessed correctly that this patient had acute chest syndrome, rather than a pleural effusion (19%), pulmonary edema (13%) or a pneumothorax (3%).

Normal Lung

Although air is commonly known as the ‘enemy of ultrasound’ for most applications, it is the operator’s ally when viewing the lungs. Normally, air in the lung impedes ultrasound waves to tissue beneath it, producing a normal artifact finding called A-lines. These horizontal, hyperechoic A-lines are a reverberation artifact of the pleural line and are a normal finding in lung ultrasound. The superficial hyperechoic lines with posterior acoustic shadowing seen at regular intervals represent ribs.

Notice that in the normal lung, lung sliding is also visualized. This shimmer of the hyperechoic pleural line, is also known as the ‘ants-marching’ sign.1

The normal lung’s A-lines will disappear when air is replaced by either fluid or consolidation beneath the pleural line of the lung. Both these processes are mediums that allow transmission of ultrasound waves resulting in the loss of A-lines and the visualization of the pathology beneath the pleura.

Consolidation

Bacteria or viruses are seen on ultrasound as consolidative processes and are associated with a loss of A-lines and disruption of the pleural line. Established bacterial consolidation is usually seen as lesions larger than 1 cm, while viral causes and early bacterial processes are thought to generate subpleural consolidations, typically lesions less than 1cm beneath the pleural line. In a recent meta-analysis of diagnostic accuracy of lung ultrasound for childhood pneumonia, lung ultrasound had a sensitivity of 96% and specificity of 93%.2

A large consolidative process is termed ‘hepatization’ of the lung because its sonographic appearance has a similar echotexture to that of hepatic tissue. It generally measures greater than 1 cm in size, and is suggestive of a bacterial cause of consolidation. Also found within this consolidative process are ‘dynamic air bronchograms,’ seen as hyperechoic lines, which represent air in the bronchioles surrounded by fluid-filled alveoli.

In sickle cell disease, patients with respiratory symptoms and a consolidative process visualized on an x-ray are diagnosed with acute chest syndrome (ACS). Current literature suggests that sickle cell disease patients presenting with respiratory signs or symptoms require a chest x-ray to help determine if ACS is present, which exposes sickle cell patients to large cumulative radiation doses over their lifetime. Acute chest syndrome on lung ultrasound is identified as a consolidation with air bronchograms, as defined above. Two recent abstracts published in 2015 have identified that lung ultrasound has a high sensitivity and specificity for detecting ACS, and questions the need for routine chest x-rays when the initial lung ultrasound screening is negative.3,4

Pleural effusions are usually seen when visualizing the base of the lungs. There is an absence of both the A-lines and the mirror image of the liver/spleen seen above the diaphragm that is present in the image of a normal lung base. The ‘mirror artifact’ is replaced by the anechoic appearance of fluid and the spine sign seen extending above the diaphragm.

Pulmonary Edema

B-lines are artifacts described as vertical hyperechoic lines that arise from the pleural line, obliterate A-lines, extend to the end of the screen and move with respiration.

B-lines are generated when there is interstitial fluid in the lung. The presence of a few B-lines can be suggestive of a bronchiolitis or viral pneumonia, but a confluence of B-lines suggests pulmonary edema, and is termed the ‘B profile.’

Think you already know all there is to know about lung ultrasound? Prove it.

If you want to see YOUR image included in the next Image of the Month, please email interesting stills and/or clips in addition to a small blurb on the patient to Lorraine Ng at PEMFellows.com@gmail.com.

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One Comment

Many times a “new infiltrate” on chest x-ray when checked on ultrasound may appear either as B-lines OR as a consolidation/hepatization. I wonder whether only the latter is true acute chest. OR perhaps the flipside- do b-lines/viral processes equally impact sickling and place patient at risk?